1. Field of the Invention
The present invention relates to a sheet-supply unit used in an image forming device such as a copy machine, a facsimile machine, or a laser printer and more particularly to a sheet-supply unit configured to supply one sheet at a time from sheets stacked in a sheet-supply portion and to use a pair of resist rollers to align the front edge of the sheet supplied toward an image forming portion.
2. Description of the Related Art
The basic configuration of conventional image forming devices, such as those used in printers and copy machines, includes a sheet-supply mechanism for supplying sheets one at a time using rotation of a sheet-supply roller; a resist roller mechanism for using a pair of resist rollers to align the front edge of sheets supplied by the sheet-supply mechanism; and a print mechanism, such as a laser-type print mechanism, for forming an image on a supplied sheet after the sheet passes through the resist roller mechanism. An electromagnetic actuator solely for sheet-supply operations is provided in the sheet-supply mechanism. Also, an electro-magnetic actuator solely for temporarily stopping drive of the resist rollers is provided to the resist roller mechanism.
An example of such a conventional image forming device will be explained with reference to a sheet-supply mechanism 110 provided to a typical laser printer 100 shown in FIGS. 1 and 2. A sheet-supply roller 111 is provided for supplying, one sheet at a time, recording sheets P contained in a sheet-supply cassette 104. A partial gear 112 and a cam plate 113 are attached integrally to an end of the sheet-supply roller 111. The cam plate 113 includes a spring receiving cam 114 and a stop cam 115 formed integrally with each other. A stop lever 117 is swingably fixed to a cover of the laser printer 100. The stop lever 117 has a engagement portion 117a for engaging with an engagement protrusion 115a of the stop cam 115. A pulling spring 119 constantly urges the stop lever 117 into a stop condition wherein the engagement portion 117a is where it is engagable with the engagement protrusion 115.
An edge of a coil spring 116 urgingly presses against the spring receiving cam 114 so that the partial gear 112 is resiliently urged to rotate and face its geared side into engagement with a drive gear 109, which is driven by a roller drive mechanism (not shown in the drawings). Further, an input lever 120 is swingably fixed to a side panel 103 and is capable of moving the stop lever 117 from a stop position indicated by a solid line to a stop-release position indicated by a two-dot chain line. A sheet-supply solenoid 122 for swinging the input lever 120 into a sheet-supply operation position indicated by the two-dot chain line at timing of sheet supply is fixed to the side panel 103.
Next, an explanation will be provided for a resist roller mechanism 130 provided downstream from the sheet-supply mechanism 110 in a sheet-feed direction. A first resist roller 130 is rotatably supported to the side panel 103 on a shaft. A second resist roller 131 for pressing against the first resist roller 130 is rotatably provided to the side panel 103. The first resist roller 130 receives and is driven by drive force from a transmission mechanism 133. The transmission mechanism 133 includes a plurality of planetary gears (not shown) configured so that when the rotation of a rotation gear 135 is prevented, the drive force received from the roller drive mechanism is transmitted to an output gear 134 so that the first resist roller 130 is driven, but when the rotation gear 135 is in a rotatable condition, the drive force is not transmitted to the output gear 134.
Further, a swing switch lever 136 having an engagement slat 136a engagable with the rotation gear 135 is swingably supported on a shaft to the side panel 103. A pulling spring 137 resiliently urges the engaging slat 136a into engagement with the rotation gear 135. Also, a transmission switching solenoid 138 is provided for switching the swing switch lever 136 from a transmission position shown in FIG. 1 to a non-transmission position shown in FIG. 2.
A sheet detection mechanism 140 is provided between the sheet-supply mechanism 110 and the resist roller mechanism 130. The sheet detection mechanism 140 includes a sheet detection swing lever 141 rotated to a predetermined angle by a supplied recording sheet P and a swing lever 142 swinging in association with the sheet detection swing lever 141.
As shown in FIG. 1, when a sheet is being supplied, the sheet-supply solenoid 122 is driven so that the input lever 120 swings to the sheet-supply operation position indicated by the two-dot chain line. At the same time, the stop lever 117 swings to the stop-release position indicated by the two-dot chain line. When engagement between the stop protrusion 115a of the stop cam 115 and the engagement portion 117a of the stop lever 117 is released, because the spring receiving cam 114 is urged by the spring force of the coil spring 116, the partial gear 112 is rotated counter-clockwise so its engagement side engages with the drive gear 109. At the same time, a recording sheet P is supplied by the rotating sheet-supply roller 111.
On the other hand, as shown in FIG. 2, after a predetermined time elapses directly after the start of sheet supply, the front edge of the recording sheet P reaches the pair of resist rollers 131, 132. At this point, the transmission switching solenoid 138 is driven for a short duration of time to switch the swing switch lever 136 from the transmission position to the non-transmission position. Because the drive force from the rotation gear 135, which is driven in a predetermined direction is not transmitted to the output gear 134, the pair of resist rollers 131, 132 stop rotating for the short duration of time. During this stopping period, the recording sheet P is aligned into a desired orientation. Afterward, the swing switch lever 136 is switched to the transmission position so that rotation of the pair of resistor rollers 131, 132 starts again and sheet supply operations of the recording sheet P continue.
The image forming device described above has two solenoids: one provided to sheet-supply mechanism and one provided to the resist roller mechanism. This increases the cost and size of the image forming device. Also, because two solenoids must be adjusted while being installed, assembly is time consuming.